Focus searching method and optical disc device

ABSTRACT

A focus search driving voltage corresponding to a signal surface of an optical disc is obtained on the basis of detection information from a photodetector when an objective lens is focused on the signal surface of the optical disc in the middle of raising or lowering the objective lens placed on standby at a lens midpoint between a temporarily set lens bottom point and a temporarily set lens top point according to a temporarily set lens bottom point voltage and a temporarily set lens top point voltage. Then, a lens bottom point voltage and a lens top point voltage at the time of device starting are obtained by an arithmetic operation program based on the focus search driving voltage and predetermined factors, and then a lens bottom point corresponding to the lens bottom point voltage is set to be nearer to the lens midpoint side than the temporarily set lens bottom point while a lens top point corresponding to the lens top point voltage is set to be nearer to the lens midpoint side than the temporarily set lens top point.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disc device on which a CD(Compact Disc), a hybrid SACD (Super Audio CD) and a DVD (DigitalVersatile Disc) can be selectively loaded. More particularly, theinvention relates to a focus searching method of quickly performing afocus search, in which presence or absence detection of an optical discand type detection thereof are performed, at the time of devicestarting, and an optical disc device.

2. Description of the Related Art

Generally, an optical disc has been in wide use as it enables recordinginformation signals such as video information, audio information orcomputer data on a track helically or concentrically formed on a discsubstrate at a high density and high-speed access to a desired trackwhen an information signal is recorded or reproduced from a recordedtrack.

Now, optical discs can be largely classified into a read-only type and arecordable type. In the case of the optical disc of the read-only type,a concave-convex pit row of tracks is helically or concentrically formedon a disc substrate by injection molding that uses a resin material, anda reflection film of aluminum or the like is attached on theconcave-convex pit row to form a signal surface.

On the other hand, in the case of the optical disc of the recordabletype, a track is previously formed of concave-convex grooves and landshelically or concentrically formed beforehand on a disc substrate byinjection molding that uses a resin material, and a recording film and areflection film are sequentially attached on the grooves and the landsto form a signal surface.

Then, the optical disc of the read-only type reproduces data in thefollowing manner. The signal surface is irradiated with a laser beam forreproduction which is emitted through an objective lens from an opticalpickup disposed in an optical disc device to be movable in a diameterdirection of the optical disc, and a return light beam reflected fromthe signal surface is received by a photodetector.

On the other hand, the optical disc of the recordable type records aninformation signal on the recording film of the signal surface by alaser beam for recording which is emitted through an objective lens froman optical pickup disposed in an optical disc device to be movable in adiameter direction of the optical disc, and then reproduces the signalfrom the recorded signal surface by a laser beam for reproduction as inthe above case.

Regarding compact discs (CDs) among the optical discs, there are aread-only disc on which music information has been recorded, a read-onlyCD-read only memory (CD-ROM) on which computer data has been recorded, arecordable/reproducible CD-recordable (CD-R) on which an informationsignal can be recorded only once, a recordable/reproducibleCD-rewritable (CD-RW) on which the information signal can be recorded bya plurality of times, and the like. These optical discs are treated asCDs since CD signal surfaces are formed in positions apart by about 1.2mm from beam incident surface of a disc substrate.

Further, there is a super audio CD (SACD) that employs a recentlydeveloped 1-bit direct stream digital technology. In the case of thisSACD, an HD signal surface is formed in a position apart by about 0.6 mmfrom a beam incident surface of a disc substrate, and the HD signalsurface cannot be played back by a general CD player. However, in thecase of a hybrid SACD that has a CD signal surface formed in a positionapart by about 1.2 mm from a beam incident surface of a disc substratein addition to an HD signal surface described above, the SACD is treatedas a CD based on the CD signal surface. This enables playing-back the CDsignal surface even by the general CD player.

On the other hand, regarding digital versatile discs (DVDs) higher inrecording density than CDs, there are a read-only disc for reproducing adigitized and compressed video or audio, a read-only DVD-read onlymemory (DVD-ROM) on which computer data has been recorded, arecordable/reproducible DVD-recordable (DVD-R) on which an informationsignal can be recorded only once, a recordable/reproducibleDVD-rewritable (DVD-RW) and a DVD-random access memory (DVD-RAM) onwhich the information signal can be recorded by a plurality of times,and the like. These optical discs are treated as DVDs since DVD signalsurfaces of one or two layers are formed in positions apart by about 0.6mm from a beam incident surface of a disc substrate.

Note that, for the signal surface formed on the optical disc, whilethere are a read-only type and a recordable type as described above,because a laser beam for reproduction is used when a type of an opticaldisc is detected, description below will be made focusing on a case ofreproduction.

FIGS. 1A to 1D are schematic views explaining types of optical discs:FIG.1A shows a CD, FIG.1B shows a hybrid SACD, FIG. 1C shows a DVD-SL inwhich a signal surface is a one layer type, and FIG.1D shows a DVD-DL inwhich a signal surface is a two layer type.

First, as shown in FIG. 1A, a CD (Compact Disc) 10 is constituted in afollowing manner. A disc substrate 11 is formed in a disc shape at adiameter of about 120 mm, a diameter of a center hole of 15 mm, and asubstrate thickness of about 1.2 mm by using a transparent resinmaterial. A CD signal surface 12 is formed in a position apart by about1.2 mm from a beam incident surface 11 a on the transparent discsubstrate 11 by setting a pit width and a track pitch larger than thoseof a DVD, which will be described later, and attaching a totalreflection film, and further a protective film 13 is attached on the CDsignal surface 12.

Then, in the case of playing back the CD 10 by an optical pickup (notshown) in an optical disc device, the CD signal surface 12 is irradiatedwith a laser beam L1, of which a wavelength has been narrowed by anobjective lens OB1 having a numerical aperture (NA) of 0.45 nearly to780 nm from the beam incident surface 11 a side of the transparent discsubstrate 11, and the CD signal surface 12 is played back by a returnlight reflected thereon.

Next, as shown in FIG. 1B, a super audio CD (hybrid SACD) 20 isconstituted as a hybrid optical disc in which the disc substrate 11 ofthe CD 10 is divided into two in a thickness direction, and an HD signalsurface 22 is added to a middle part of a CD signal surface 25 inaddition to a CD signal surface 25 of an upper surface side.

More specifically, the hybrid SACD 20 is constituted in the followingmanner. First and second disc substrates 21, 24 having a thickness ofabout 0.6 mm, respectively, are stuck together to form a disc of about1.2 mm in total thickness by using transparent resin materials. An HDsignal surface 22 that employs a one bit direct stream digitaltechnology is formed in a position apart by about 0.6 mm from a beamincident surface 21 a on the lower first disc substrate 21 by setting apit width and a track pitch smaller than those of the CD 10 andattaching a semi-transmissive reflection film, and a protective film 23is formed on the HD signal surface 22. A CD signal surface 25 is formedin a position apart by about 1.2 mm from the beam incident surface 21 aon the upper second disc substrate 24 by setting a pit width and a trackpitch larger and attaching a total reflection film as in the case of theCD 10, and further attaching a protective film 26 on the CD signalsurface 25.

In the case of playing back the hybrid SACD 20, the HD signal surface 22is irradiated with a laser beam L2, of which a wavelength has beennarrowed by an objective lens OB2 having a numerical aperture (NA) of0.5 to 0.6 to nearly 650 nm, from the beam incident surface 21 a side ofthe lower transparent first disc substrate 21, and the HD signal surface22 is played back by a return light reflected thereon. The CD signalsurface 25 is irradiated with a laser beam L1, of which a wavelength hasbeen narrowed by an objective lens OB1 having a numerical aperture (NA)of 0.45 to nearly 780 nm and which has been transmitted through the HDsignal surface 22, from the beam incident surface 21 a side, and the CDsignal surface 25 is played back by a return light reflected thereon.

Next, as shown in FIG. 1C, a digital versatile disc-single layer(DVD-SL) 30 in which a signal surface is one layer type is constitutedin the following manner. A disc substrate 31 having a thickness of about0.6 mm and a reinforcing disc substrate 34 having a thickness of about0.6 mm are stuck together by use of a resin material to form a dischaving about 1.2 mm in total thickness. A DVD signal surface 32 isformed in a position apart by about 0.6 mm from a beam incident surface31 a on the lower disc substrate 31 by setting a pit width and a trackpitch smaller than those of the CD 10 and attaching a total reflectionfilm, and a protective film 33 is formed on the DVD signal surface 32.

Then, in the case of playing back the DVD-SL 30 in which the signalsurface is one layer type, the DVD signal surface 32 is irradiated witha laser beam L2, of which a wavelength has been narrowed by an objectivelens OB2 of a numerical aperture (NA) of 0.5 to 0.6 to nearly 650 nm,from the beam incident surface 31 a side of the transparent discsubstrate 31, and the DVD signal surface 32 is played back by a returnlight reflected thereon.

Next, as shown in FIG. 1D, a digital versatile disc-dual layer (DVD-DL)40 in which a signal surface is two layer type is constituted in thefollowing manner. First and second disc substrates 41, 46 set to about0.6 mm in thickness are stuck together to form a disc of about 1.2 mm intotal thickness by using transparent resin materials. A first DVD signalsurface 42 is formed in a position apart by about 0.6 mm from a beamincident surface 41 a on the lower first disc substrate 41 by setting apit width and a track pitch smaller than those of the CD 10 andattaching a semi-transmissive reflection film, and a protective film 43is formed on the first DVD signal surface 42. A second DVD signalsurface 45 is formed on the upper second disc substrate 46 close to thefirst DVD signal surface 42 by setting a pit width and a track pitchsmaller than those of the CD 10 and attaching a total reflection film,and a protective film 44 is attached below the second DVD signal surface45.

Then, in the case of playing back the DVD-DL 40 in which the signalsurface is two-layer type, the first DVD signal surface 42 or the secondDVD signal surface 45 is irradiated with a laser beam L2, of which awavelength has been narrowed by an objective lens OB2 of a numericalaperture (NA) of 0.5 to 0.6 to nearly 650 nm, from the beam incidentsurface 41 a side of the transparent first disc substrate 41, and thefirst DVD signal surface 42 or the second DVD signal surface 45 isplayed back by a return light reflected thereon.

Incidentally, there are a device and a method for identifying an opticalcarrier, which can identify a type of an optical disc by selectivelyloading one of the CD 10, the hybrid SACD 20 and the DVD-SL 30 in whichthe signal surface is the one layer type, and using a detection signalfrom a photodetector disposed in an optical pickup (e.g., see pp. 2 to6, FIG.3 of Japanese Patent Application Laid-Open No.2000-293932).

FIG. 2 shows principle waveform charts for explaining a device and amethod for identifying a carrier according to a conventional art.

The conventional carrier identifying device and method shown in FIG. 2are disclosed in the above Japanese Patent Application Laid-Open No.2000-293932. Here, description will be made briefly by referring to thisPublication and FIGS. 1A to 1D and FIG. 2.

According to the conventional optical carrier identifying device andmethod disclosed in the Japanese Patent Application Laid-OpenNo.2000-293932, as shown in (a) of FIG. 2, an objective lens disposed inan optical pickup is raised or lowered by a focus search driving signalrelative to an optical disc mounted on a turntable.

During playing-back of the optical disc, a return light from a signalsurface of the optical disc is received by a plurality of photodetectionareas A to D in a photodetector disposed in the optical pickup and,subsequently, photodetection amounts of the plurality of photodetectionareas A to D are all added to generate an all sum signal AS (describedas a pull-in signal PI in the Publication). At this time, all sum signalAS=(A+B+C+D) is set.

Now, as shown in (b) of FIG. 2, in the case of playing back the CD 10 asan optical disc, since there is a roughly 1.2 mm distance from the beamincident surface 11 a of the disc substrate 11 to the CD signal surface12, all sum signals AS appear at positions I, III of the beam incidentsurface 11 a and the CD signal surface 12. A identification signal DDsimilar to that shown in (c) of FIG. 2 is obtained when comparison ismade to determine whether values of the all sum signals AS exceed athreshold value TH or not. Then, a pulse interval t1 between the two allsum signals AS is measured to identify the optical disc as a CD.

Next, as shown in (d) of FIG. 2, in the case of playing back the DVD-SL30 in which the signal surface is one layer type as an optical disc,since there is a roughly 0.6 mm distance from the beam incident surface31 a of the first disc substrate 31 to the DVD signal surface 32, allsum signals AS appear at positions I, II of the beam incident surface 31a and the DVD signal surface 32. A identification signal DD similar tothat shown in (e) of FIG. 2 is obtained when comparison is made todetermine whether values of the all sum signals AS exceed a thresholdvalue TH or not. Then, a pulse interval t2 between the two all sumsignals AS is measured to identify the optical disc as a DVD. In thisevent, for example, if time tTH is held as a reference value which is anintermediate value between the measured values t1 and t2, a measuredvalue tx is compared with the time tTH to determine whether the measuredvalue tx is t1 or t2. That is, it is possible to identify whether theoptical disc is a CD 10 or a DVD-SL 30.

Next, as shown in (f) of FIG. 2, in the case of playing back the hybridSACD 20 as an optical disc, since the HD signal surface 22 is at aposition of about 0.6 mm from the beam incident surface 21 a of thefirst disc substrate 21, and the CD signal surface 25 is located apartby about 0.6 mm from this HD signal surface 22, all sum signals ASappear at positions I, II, III of the beam incident surface 21 a, the HDsignal surface 22 and the CD signal surface 25. A identification signalDD similar to that shown in (g) of FIG. 2 is obtained when comparison ismade to determine whether values of the all sum signals AS exceed athreshold value TH or not. Then, pulse intervals t3, t4 among the threeall sum signals AS are measured to identify the optical disc as a hybridSACD.

Meanwhile, according to the optical carrier identifying device andmethod disclosed in the Japanese Patent Application Laid-Open No.2000-293932, when the types of the CD 10, the DVD-SL 30 in which thesignal surface is one layer type, and the hybrid SACD 20 are identified,a laser beam is focused on a signal surface of an optical disc in themiddle of raising or lowering the objective lens placed on standby at alens midpoint between a lower lens bottom point and an upper lens toppoint based on a focus search driving signal. However, generally sincethe lens bottom point of the objective lens is set to a lower positionsufficiently apart from the optical disc while the lens top point of theobjective lens is set to a position slightly before the objective lensabuts on a beam incident surface of the optical disc, the movingdistance of the objective lens at the time of the focus search is longand therefore it takes long time for the objective lens to move, whichis a problem.

SUMMARY OF THE INVENTION

In view of the above, there is a demand for an optical disc device and afocus searching method capable of quickly shift to a data reproductionoperation after a focus search operation by shortening the movingdistance of the objective lens at the time of focus search and thusreducing a moving time of the objective lens.

In order to achieve the foregoing object, there is provided a focussearching method in which a laser beam is irradiated on an optical discfrom a beam incident surface side thereof through an objective lens, anda return light from a signal surface of the optical disc is received bya photodetector in the middle of raising or lowering the objective lensplaced on standby at a lens midpoint between a lower lens bottom pointand an upper lens top point based on a focus search driving signalduring focus searching, and whether the objective lens is focused on thesignal surface of the optical disc while keeping a predetermined workingdistance to the beam incident surface of the optical disc is determinedon the basis of the detection information from the photodetector, themethod comprising the steps of: storing in advance a temporarily setlens bottom point voltage corresponding to a temporarily set lens bottompoint temporarily set at a lower position that has more sufficient roomthat a predetermined working distance of the objective lens, and atemporarily set lens top point voltage corresponding to a temporarilyset lens top point temporarily set at a position slightly before theobjective lens abuts on the beam incident surface of the optical disc;obtaining a focus search driving voltage corresponding to the signalsurface of the optical disc based on the detection information from thephotodetector when the objective lens is focused on the signal surfaceof the optical disc in the middle of raising or lowering the objectivelens placed on standby at the lens midpoint between the temporarily setlens bottom point and the temporarily set lens top point based on thetemporarily set lens bottom point voltage and a temporarily set lens toppoint voltage; and obtaining a lens bottom point voltage and a lens toppoint voltage at the time of device starting by an arithmetic operationprogram based on the focus search driving voltage and a predeterminedfactor, and setting the lens bottom point corresponding to the lensbottom point voltage to be nearer to the lens midpoint side than thetemporarily set lens bottom point while setting the lens top pointcorresponding to the lens top point voltage to be nearer to the lensmidpoint side than the temporarily set lens top point.

Furthermore, in order to achieve the foregoing object, there is providedan optical disc device in which a laser beam is irradiated on an opticaldisc from a beam incident surface side thereof through an objectivelens, and a return light from a signal surface of the optical disc isreceived by a photodetector in the middle of raising or lowering theobjective lens placed on standby at a lens midpoint between a lower lensbottom point and an upper lens top point based on a focus search drivingsignal during focus searching, and whether the objective lens is focusedon the signal surface of the optical disc while keeping a predeterminedworking distance to the beam incident surface of the optical disc isdetermined on the basis of the detection information from thephotodetector, the device comprising: storing means for storing inadvance a temporarily set lens bottom point voltage corresponding to atemporarily set lens bottom point temporarily set at a lower positionthat has more sufficient room that a predetermined working distance ofthe objective lens, and a temporarily set lens top point voltagecorresponding to a temporarily set lens top point temporarily set at aposition slightly before the objective lens abuts on the beam incidentsurface of the optical disc; focus search driving signal generatingmeans for obtaining a focus search driving voltage corresponding to thesignal surface of the optical disc based on the detection informationfrom the photodetector when the objective lens is focused on the signalsurface of the optical disc in the middle of raising or lowering theobjective lens placed on standby at the lens midpoint between thetemporarily set lens bottom point and the temporarily set lens top pointbased on the temporarily set lens bottom point voltage and a temporarilyset lens top point voltage; and arithmetic operating means for obtaininga lens bottom point voltage and a lens top point voltage at the time ofdevice starting by an arithmetic operation program based on the focussearch driving voltage and a predetermined factor, and setting the lensbottom point corresponding to the lens bottom point voltage to be nearerto the lens midpoint side than the temporarily set lens bottom pointwhile setting the lens top point corresponding to the lens top pointvoltage to be nearer to the lens midpoint side than the temporarily setlens top point.

The nature, principle and utility of the invention will become moreapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1D are schematic views explaining types of optical discs,FIG. 1A showing a CD, FIG. 1B showing a hybrid SACD, FIG. 1C showing aDVD-SL in which a signal surface is a 1-layer type, and FIG. 1D showinga DVD-DL in which a signal surface is a 2-layer type;

FIG. 2 shows principle waveform charts explaining a device and a methodfor identifying a carrier according to a conventional art;

FIG. 3 is a constitutional view showing an entire constitution of anoptical disc device according to the present invention;

FIG. 4 is a circuit diagram showing a circuit for generating a TR signalof a CD, an FE signal of the CD or a DVD, an AS signal of the CD or theDVD, and an RF signal of the CD in a photodetector signal processingcircuit shown in FIG. 3;

FIG. 5 is a circuit diagram showing a circuit for generating an RFsignal of the DVD, and a TR signal of the DVD in the photodetectorsignal processing circuit shown in FIG. 3;

FIG. 6 is a schematic view explaining a working distance of an objectivelens;

FIG. 7 is a flowchart explaining an operation of setting a working rangeof the objective lens by using a reference CD in the focus searchingmethod according to the present invention;

FIG. 8 is a schematic operation view explaining the operation of settingthe working range of the objective lens by using the reference CD in thefocus searching method according to the present invention;

FIG. 9 is a schematic operation view explaining an operation ofacquiring a focus search driving voltage corresponding to a DVD signalsurface by using a reference DVD after the working range of theobjective lens is set in the focus searching method according to thepresent invention;

FIG. 10 is a flowchart (1) of identifying a type of an unknown opticaldisc by starting a semiconductor laser for DVD first;

FIG. 11 is a flowchart (2) of identifying the type of the unknownoptical disc by starting the semiconductor laser for DVD first;

FIG. 12 is a schematic operation view explaining a focus searchingoperation on the unknown optical disc by the objective lens;

FIG. 13 is a schematic operation view showing the operation ofidentifying the type of the unknown optical disc when focus searching iscarried out by using the semiconductor laser for DVD;

FIGS. 14A and 14B are schematic views for explaining the operation ofidentifying the type of the unknown optical disc based on an envelopetrack state of an RF signal, FIG. 14A showing a case of a CD signalsurface of a hybrid SACD, and FIG. 14B showing a case of a DVD-SL, aDVD-DL;

FIG. 15 is a flowchart (1) of identifying the type of the unknownoptical disc by starting a semiconductor laser for CD first; and

FIG. 16 is a flowchart (2) of identifying the type of the unknownoptical disc by starting a semiconductor laser for CD first; and

FIG. 17 is a flowchart (3) of identifying the type of the unknownoptical disc by starting the semiconductor laser for CD first.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, detailed description will be made of an embodiment of afocus searching method and an optical disc device according to thepresent invention with reference to FIGS. 3 to 16. Note that, in thedescription below, members similar to those described above withreference to FIGS. 1A to 1D will be denoted by the same referencenumerals.

FIG. 3 is a block diagram showing an entire constitution of an opticaldisc device according to the present invention. FIG. 4 is a circuitdiagram showing a circuit for generating a TR signal of a CD, an FEsignal of the CD or a DVD, an AS signal of the CD or the DVD, and an RFsignal of the CD in a photodetector signal processing circuit shown inFIG. 3. FIG. 5 is a circuit diagram showing a circuit for generating anRF signal of the DVD, and a TR signal of the DVD in the photodetectorsignal processing circuit shown in FIG. 3.

As shown in FIG. 3, in an optical disc device 50 of the presentinvention, the CD 10, the hybrid SACD 20, the DVD-SL 30 in which thesignal surface is the one layer type, and the DVD-DL 40 in which thesignal surface is the two-layer type described above with reference toFIGS. 1A to 1D can be selectively loaded on a turntable (not shown) asthe optical discs, and these various optical discs can be rotatedintegrally with the turntable by an unillustrated spindle motor. In theoptical disc device 50, priority is given to the DVD-SL 30 and theDVD-DL 40 as main use, while the CD 10 and the hybrid SACD 20 are set assub-use. The hybrid SACD 20 that has an HD signal surface 22 and a CDsignal surface 25 is treated simply as a CD. Thus, the optical discdevice 50 is provided inexpensively.

In the optical disc device 50, a control section 51 is disposed tocontrol the entire device by using a microcomputer. In this case, thecontrol section 51 includes the following functional sections: a memorysection 51 a, an arithmetic operation section 51 b, a focus searchdriving signal generation section 51 c, an optical disc typeidentification section 51 d, and a program section 51 e. These sectionsin the control section 51 will be described as necessary.

Below the optical disc, an optical pickup 60 is disposed to be movablein a diameter direction of the optical disc by the unillustrated spindlemotor.

The optical pickup 60 includes a semiconductor laser 63 for CD forirradiating the CD 10 and the hybrid SACD 20 with a laser beam of whichwavelength is near 780 nm, and a semiconductor laser 64 for DVD forirradiating the DVD-SL 30 and the DVD-DL 40 with a laser beam of whichwavelength is near 650 nm. These semiconductor lasers 63 and 64 areinstalled to be very slightly apart from each other left and rightsetting an optical axis of an objective lens 73 as a center on asemiconductor substrate (Si substrate) 62 disposed in a lower side of anoptical pickup casing 61.

On both left and right sides of the semiconductor laser 63 for CD andthe semiconductor laser 64 for DVD, a plurality of photodetectors 65 to70 are integrally formed on the semiconductor substrate 62.

Additionally, a hologram 71 is disposed above the semiconductor laser 63for CD and the semiconductor laser 64 for DVD. Further, the objectivelens 73 attached to a lens holder 72 is supported above the hologram 71to be swingable in a tracking direction and a focusing direction throughan unillustrated suspension wire. In this case, the objective lens 73 isformed to set a numerical aperture (NA) of 0.45 for the CD 10 and thehybrid SACD 20, and a numerical aperture (NA) of 0.5 to 0.6 for theDVD-SL 30 and the DVD-DL 40. Such an objective lens 73 may be referredto as a special objective lens.

Moreover, a tracking coil 74 and a focusing coil 75 are fixed to anouter peripheral surface of the lens holder 72 to which the objectivelens 73 has been attached. The tracking coil 74 is for controlling theobjective lens 73 integrally with the lens holder 72 in the trackingdirection, while the focusing coil 75 is for controlling the objectivelens 73 integrally with the lens holder 72 in the focusing direction.

At the time of starting the optical disc device 50, the priority isgiven to the DVD-SL 30 and the DVD-DL 40 in the optical disc device 50as described above. Accordingly, a laser driving circuit 52 is actuatedby a command from the control section (microcomputer) 51 and then alaser driving current LI generated in the laser driving circuit 52 isapplied to the semiconductor laser 64 for DVD through a switch SW 1. Alaser beam of near 650 nm emitted from the semiconductor laser 64 forDVD is transmitted through the hologram 71 to enter the objective lens73. The laser beam narrowed by the objective lens 73 is irradiated ontoa signal surface of an optical disc. Subsequently, a return lightreflected on the signal surface of the optical disc is passed throughthe objective lens 73, and diffracted to a plurality of optical paths bythe hologram 71 to be received by the plurality of photodetectors 65 to70.

In this event, at the time of starting the optical disc device 50, thesemiconductor laser 64 for DVD is started first, and the laser beam fromthe semiconductor laser 64 for DVD is used to identify a type of theoptical disc as described later. When a result of the identificationshows that the optical disc is a CD, the semiconductor laser 63 for CDis started.

Incidentally, an operation opposite to the above is possible. That is,at the time of starting the optical disc device 50, the Semiconductorlaser 63 for CD is started first, a laser beam from the semiconductorlaser 63 for CD is used to identify a type of the optical disc and, whena result of the identification shows that the disc is a DVD, thesemiconductor laser 64 for DVD is started.

Additionally, photodetector detection signals PDS obtained by receivingthe return light reflected on the signal surface of the optical disc atthe plurality of photodetectors 65 to 70 disposed in the optical pickup60 are inputted to a photodetector signal processing circuit 53 togenerate a tracking error signal TE (may be referred to as a TE signalhereinafter), a focusing error signal FE (may be referred to as an FEsignal hereinafter), a data reproducing signal RF (may be referred to asan RF signal hereinafter), and an all sum signal AS (may be referred toas an AS signal hereinafter) therein as described later.

Note that when the signals are processed in the photodetector signalprocessing circuit 53, the signals are processed for the CD when the CD10 or the hybrid SACD 20 is played back and for the DVD when the DVD-SL30 or the DVD-DL 40 is played back in accordance with a command from thecontrol section 51.

Now, the signal processing in the photodetector signal processingcircuit 53 will be described more specifically. The plurality ofphotodetectors disposed in the optical pickup 60 include a pair ofsub-photodetectors 66, 67 disposed front and back of a 4-division typephotodetector 65 in the tracking direction to obtain a TR signal of aCD, one 4-division type photodetector 65 disposed to obtain an FEsignal, an AS signal and an RF signal of the CD, and a pair of4-division type photodetectors 68, 69 disposed to obtain an FE signaland an AS signal of a DVD as shown in FIG. 4, and one 4-division typephotodetector 70 disposed to obtain an RF signal and a TR signal of theDVD as shown in FIG. 5.

First, as shown in FIG. 4, the TR signal of the CD is obtained by usinga well-known 3-beam method to input photodetection outputs of the pairof sub-photodetectors 66, 67 through resistors 81, 82 to a balancer 83,and detecting a difference between both outputs at the balancer 83.

The all sum signal AS that is a main part of the present inventionincludes an AS signal of the CD and an AS signal of the DVD, and isobtained by selectively switching the AS signals thereof by switchesSW3, SW4. In this event, the switches SW3, SW4 are switched to obtainthe AS signal of the DVD first at the time of starting the optical discdevice 50. Subsequently, the switches SW3, SW4 are switched to obtainthe AS signal of the CD when a type of the optical disc is identified asa CD.

The AS signal of the CD is obtained by using a well-known push-pullmethod to add all photodetection amounts of 4-division photodetectionareas A to D arranged in a cross shape in one 4-division typephotodetector 65, and a signal band of the AS signal of the CD is 100KHz or lower.

That is, since the FE signal of the CD (described later) issimultaneously obtained, division is first made into an (A+D) area and a(B+C) area, and the AS signal of the CD is obtained as (A+B+C+D) byadding all photodetection outputs of the (A+D) area and the (B+C) areathrough the switches SW3, SW4 at an adder 84.

On the other hand, the AS signal of the DVD is obtained by using awell-known spot size method (SSD method) to add all photodetectionamounts of 4-division photodetection areas A to D arranged in parallelin the pair of 4-division type photodetectors 68, 69, and a signal bandof the AS signal of the DVD is 100 KHz or lower.

That is, since the FE signal of the DVD (described later) issimultaneously obtained, division is first made into a first group of{(B+C) area of 4-division type photodetector 68}+{(A+D) of 4-divisiontype photodetector 69} and a second group of {{A+D} area of 4-divisiontype photodetector 68}+{(B+C) of 4-division type photodetector 69}.Then, the AS signal of the DVD is obtained as {(A+B+C+D) of 4-divisiontype photodetector 68}+{(A+B+C+D) of 4-division type photodetector 69}by adding all photodetection outputs of the first and second groupsthrough the switches SW3, SW4 at the adder 84.

The FE signal of the CD or the DVD is obtained by inputting outputs fromthe switches SW3 and SW4, connected to the 4-division type photodetector65 or the pair of 4-division type photodetectors 68, 69, to a balancer85, and detecting a difference between both outputs at the balancer 85.

Additionally, the RF signal of the CD is obtained by adding allphotodetection amounts of the photodetection areas A to D of the4-division type photodetector 65. However, the RF signal is a signal ofan MHz order having a different signal band from the all sum signal ASof the CD. Here, the RF signal is obtained by adding all photodetectionoutputs of the (A+D) area and the (B+D) area of the 4-division typephotodetector 65 through HPFs 86, 87 at an adder 88.

Next, as shown in FIG. 5, the RF signal of the DVD is obtained by addingall photodetection amounts of the photodetection areas A to D of the4-division type photodetector 70, and a signal band thereof is an MHzorder. That is, the RF signal of the DVD is obtained by adding allphotodetection outputs of the 4-division photodetection areas A to Darranged in a cross shape in the 4-division type photodetector 70through capacitors 91 to 94 and HPFs 95 to 98 at an adder 99.

Further, the TR signal of the DVD is obtained in the following manner.The photodetection outputs of the 4-division photodetection areas A to Darranged in the cross shape in the 4-division type photodetector 70 arepassed through the capacitors 91 to 94, equalizer amplifiers 100 to 103,HPFs 104 to 107, and operational amplifiers 108 to 111. An output of theoperational amplifier 108 corresponding to the A area and an output ofthe operational amplifier 109 corresponding to the C area are inputtedto a first differential phase detector 112, and an output of theoperational amplifier 110 corresponding to the D area and an output ofthe operational amplifier 111 corresponding to the B area are inputtedto a second differential phase detector 113. Then, outputs of the firstand second differential phase detectors 112, 113 are subtracted by asubtracter 114.

Returning to FIG. 3, at the time of reproducing data from an opticaldisc by rotating the same at a high speed (referred to as during datareproduction of the optical disc hereinafter), the tracking error signalTE obtained in the photodetector signal processing circuit 53 isinputted to a tracking control circuit 54, and a tracking control signalTE CONT generated therein is supplied to the tracking coil 74 attachedto the lens holder 72. Accordingly, the objective lens 73 is controlledintegrally with the lens holder 72 in the tracking direction withrespect to the optical disc by a magnetic force of the tracking coil 74and an unillustrated magnet.

Moreover, during the data reproduction of the optical disc, the focuserror signal FE obtained in the photodetector signal processing circuit53 is inputted to a focus control circuit 55, and a focus control signalFE CONT generated therein is supplied through a switch SW2 to the focuscoil 75 attached to the lens holder 72. Accordingly, the objective lens73 is controlled integrally with the lens holder 72 in the focusingdirection with respect to the optical disc by a magnetic force of thefocus coil 75 and an unillustrated magnet.

Further, the focus error signal FE obtained in the photodetector signalprocessing circuit 53 is inputted to the arithmetic operation section 51b in the control section 51, and determination is made as to whether again of a signal system is increased or not based on a peak-peak (p-p)value of the focus error signal FE during type identification of theoptical disc. This operation will be described later, and thusexplanation thereof is omitted here.

During the data reproduction of the optical disc, the data reproducingsignal RF obtained in the photodetector signal processing circuit 53 isinputted to an RF signal demodulation circuit 56, and inside thecircuit, one of a CD signal processing section 56 a and a DVD signalprocessing section 56 b is actuated based on a command from the controlsection 51 to demodulate and output the data reproducing signal RFcorresponding to the type of the optical disc based on a predeterminedformat.

Further, the data reproducing signal RF obtained in the photodetectorsignal processing circuit 53 is inputted to the arithmetic operationsection 51 b in the control section 51, and a track state is detectedfrom an envelope of the data reproducing signal RF to identify a DVD ora CD. However, this operation will be described later, and thusexplanation thereof is omitted here.

Next, description will be made of an operation of setting a workingrange of the objective lens 73, which is a main part of the presentinvention, during focus searching on the optical disc by the objectivelens 73 with reference to FIGS. 6 to 9.

FIG. 6 is a schematic view for explaining a working distance of theobjective lens: (a) in the figure shows a case of the DVD-SL, (b) showsa case of the CD, and (c) shows a case of the hybrid SACD. FIG. 7 is aflowchart for explaining an operation of setting a working distance ofthe objective lens by using a reference CD. FIG. 8 is a schematicoperation view for explaining the operation of setting the working rangeof the objective lens by using the reference CD. FIG. 9 is a schematicoperation view for explaining an operation of obtaining a focus searchdriving voltage corresponding to a DVD signal surface by using areference DVD after the working range of the objective lens is set.

Note that, description below is made regarding a case in which thesemiconductor laser 64 for DVD is started first. However, the inventionis not limited to this case, and the semiconductor laser 63 for CD maybe started first as long as the operation is based on the same technicalidea.

The working distance of the objective lens 73 disposed in the opticalpickup 60 will be described before explanation of the operation ofsetting the working range thereof. As shown in (a) of FIG. 6, when theobjective lens 73 is focused on the DVD signal surface 32 of the DVD-SL30, a distance between a center of the objective lens 73 and the beamincident surface 31 a of the DVD-SL 30, i.e., a working distance,becomes WD1 in design.

Moreover, as shown in (b) of FIG. 6, when the objective lens 73 isfocused on the CD signal surface 12 of the CD 10, a distance between thecenter of the objective lens 73 and the beam incident surface 11 a ofthe CD 10, i.e., a working distance, becomes WD2 in design. In the caseof the CD 10, the objective lens 73 is raised more by ΔWD toward thebeam incident surface 11 a side of the CD 10 than that in the case ofthe DVD-SL 30.

Further, as shown in (c) of FIG. 6, when the objective lens 73 isfocused on the CD signal surface 25 of the hybrid SACD 20, a workingdistance is similar to that in the case of the CD 10. Pulling-in isexecuted on the CD signal surface 25 by the objective lens 73, while nopulling-in is executed on the HD signal surface 22 by the objective lens73.

Next, description will be made of working range setting of the objectivelens 73 during focus searching with reference to FIGS. 3, 7 and 8. Theworking range setting operation of the objective lens 73 is carried outbefore the optical disc device 50 is shipped from a factory.

Here, as shown in FIG. 3, during focus searching executed before thedata signal reproducing operation of the optical disc, a focus searchdriving signal FDS is generated by the focus search driving signalgeneration section 51 c disposed in the control section 51, and thefocus search driving signal FDS is supplied through the switch SW2 tothe focus coil 75 attached to the lens holder 72. Accordingly, theobjective lens 73 is driven integrally with the lens holder 72 in thefocusing direction with respect to the optical disc in accordance withthe focus search driving signal FDS.

While the focus search driving signal FDS is not applied to the focuscoil 75 from the focus search driving signal generation section 51 cdisposed in the control section 51, the objective lens 73 has reached aposition (natural position) of a lens midpoint as shown in FIG. 8.

When focus searching is carried out on the optical disc by the objectivelens 73, a laser beam is focused on the signal surface of the opticaldisc in the middle of raising or lowering the objective lens 73 placedon standby at the lens midpoint between a lower lens bottom point and anupper lens top point by a focus search driving signal. However, in thecase of a constitution in which the CD 10, the hybrid SACD 20, theDVD-SL 30 and the DVD-DL 40 can be selectively loaded, generally, thelens bottom point of the objective lens 73 is set on a lower positionthat has more sufficient room than the working distance WD1 (FIG. 6) forthe DVD-SL 30, while the lens top point of the objective lens 73 is seton a position slightly before abutting on the beam incident surface ofthe optical disc. Consequently, a moving range of the objective lens 73is large during focus searching, thus extending moving time thereof.

Therefore, in the present invention, a focus search algorithm has beendeveloped to enable quick transfer to a data reproducing operation afterfocus searching by setting a moving range of the objective lens 73 smallduring focus searching to shorten moving time thereof.

That is, as shown in FIGS. 7 and 8, in the case of setting a movingrange of the objective lens 73 during focus searching, a temporarily setlens bottom point voltage a and a temporarily set lens top point voltageα are temporarily set in step S1. In other words, a temporarily set lensbottom point corresponding to the temporarily set lens bottom pointvoltage α is temporarily set on a position that has more sufficient roomthan the working distance WD1 (FIG. 6) for the DVD-SL 30 as in theabove-described general case. A temporarily set lens top pointcorresponding to the temporarily set lens top point voltage β is alsotemporarily set on a position slightly before abutting on the beamincident surface of the optical disc as in the above-described generalcase. Accordingly, a moving range of the objective lens 73 becomes alarge value from the temporarily set lens bottom point to thetemporarily set lens top point during the temporary setting. In thisevent, if a focus search driving voltage corresponding to the lensmidpoint (natural position) of the objective lens 73 is a referencevoltage 0, a voltage value on the lens bottom point side becomes minus(−), and a voltage value on the lens top point side becomes plus (+).

Next, in step S2, a reference CD 10 is prepared first in which a CDsignal surface 12 is located at a position of about 1.2 mm from a beamincident surface 11 a. The CD 10 is loaded on a turntable (not shown),and the semiconductor laser 64 for DVD is started in a nonrotated stateof the CD 10 to irradiate an innermost peripheral side of the CD 10 witha laser beam narrowed by the objective lens 73 from the beam incidentsurface 11 a side of the CD 10. Here, since an all sum signal valueAS-cd of a return light reflected on the CD signal surface is used inthe case of setting the moving range of the objective lens 73, the CD 10in which the CD signal surface 12 has been formed is used as a referenceoptical disc.

Next, in step S3, the objective lens 73 placed on standby at the lensmidpoint is lowered to the temporarily set lens bottom point inaccordance with the temporarily set lens bottom point voltage α whilethe CD 10 in the rotation stopped state is irradiated with a laser beamfrom the objective lens 73. Then, the objective lens 73 is raised fromthe temporarily set lens bottom point toward the temporarily set lenstop point in accordance with the temporarily set lens top point voltageβ. Note that, an operation opposite to the above is possible. That is,the objective lens 73 placed on standby at the lens midpoint may beraised to the temporarily set lens top point, and then the objectivelens 73 may be lowered from the temporarily set lens top point towardthe temporarily set lens bottom point.

Next, in step S4, if an all sum signal AS from the photodetector signalprocessing circuit 53 is inputted to the arithmetic operation section 51b in the control section 51 to be monitored in the middle of raising theobjective lens 73, a small all sum signal value AS-beamin is firstobtained at the position of the beam incident surface 11 a of the CD 10.When the objective lens 73 is raised more, a large all sum signal valueAS-cd is obtained at the position of the CD signal surface 12. In thisevent, when the large all sum signal value AS-cd is obtained at theposition of the CD signal surface 12 of the CD 10, it means that theobjective lens 73 has been focused by keeping a predetermined workingdistance to the beam incident surface 11 a of the CD 10.

Next, in step S5, the all sum signal value AS-cd obtained at theposition of the signal surface 12 is inputted to the focus searchdriving signal generation section 51 c in the control section 51. Afocus search driving voltage R corresponding to the all sum signal valueAS-cd is obtained to be stored in the memory section 51 a in the controlsection 51. This focus search driving voltage R is used for setting amoving range of the objective lens 73 and identifying a type of theoptical disc, which will be described later.

Subsequently, in step S6, the arithmetic operation section 51 b of thecontrol section 51 calculates a lens bottom point voltage γ and a lenstop point voltage δ at the time of starting based on the focus searchdriving voltage R corresponding to the all sum signal value AS-cd at theposition of the CD signal surface 12 stored in the memory section 51 aand a predetermined factor by using a calculation program from theprogram section 51 e of the control section 51. Then, the lens bottompoint voltage γ and the lens top point voltage δ at the time of startingwhich have been obtained by a learning effect based on the focus searchdriving voltage R corresponding to the position of the CD signal surface12 are stored in the memory section 51 a.

Here, in the case of obtaining the lens bottom point voltage γ and thelens top point voltage δ at the time of starting by calculation, thepredetermined factor is sensitivity of the focus coil 75, surfacewobbling of the unillustrated turntable, a surface wobbling permissiblevalue of the optical disc or the like.

The lens bottom point corresponding to the lens bottom point voltage γat the time of starting obtained by the calculation is nearer to thelens midpoint side than the temporarily set lens bottom pointcorresponding to the temporarily set lens bottom point voltage α. Thelens top point corresponding to the lens top point voltage δ at the timeof starting obtained by the calculation is nearer to the lens midpointside than the temporarily set lens top point corresponding to thetemporarily set lens top point voltage β. Thus, a moving range of theobjective lens 73 at the time of starting becomes smaller than thetemporarily set moving range. As a result, time necessary for focussearching is shortened, and quick transfer can be made to a datareproducing operation after focus searching.

Note that, regarding setting of a working range of the objective lens73, the operation before shipping from the factory has been described inthis embodiment. However, a constitution is employed in which changes ofthe optical disc device 50 with time after shipping from the factory,characteristics of the optical disc to be used, etc., are learned, and aworking range of the objective lens 73 can be set again automaticallybased on learning effects by using a program of the microcomputer.

Next, as shown in FIG. 9, after setting of the lens bottom point voltageγ and the lens top point voltage δ at the time of starting, a focussearch driving voltage Q corresponding to an all sum signal value AS-dvdon a DVD signal surface 32 is obtained by using a reference DVD-SL 30 inwhich the DVD signal surface 32 is located at a position of about 0.6 mmfrom the beam incident surface 31 a. The focus search driving voltage Qis stored in the memory section 51 a of the control section 51. Thisfocus search driving voltage Q is used for identifying a type of theoptical disc, which will be described later.

Further, a description will be made of operations of detecting presenceof an optical disc and identifying a type thereof during focus searchingon the optical disc by the objective lens 73, which are main parts ofthe present invention, with reference to FIGS. 10 to 16.

FIG. 10 is a flowchart (1) of identifying a type of an unknown opticaldisc by starting a semiconductor laser for DVD first. FIG. 11 is aflowchart (2) of identifying the type of the unknown optical disc bystarting the semiconductor laser for DVD first. FIG. 12 is a schematicoperation view explaining a focus searching operation on the unknownoptical disc by the objective lens. FIG. 13 is a schematic operationview showing the operation of identifying the type of the unknownoptical disc when focus searching is carried out by using thesemiconductor laser for DVD. FIGS. 14A and 14B are schematic views forexplaining the operation of identifying the type of the unknown opticaldisc based on an envelope track state of an RF signal: FIG. 14A shows acase of a CD signal surface of a hybrid SACD, and FIG. 14B shows a caseof a DVD-SL, a DVD-DL.

First, when focus searching on the unknown optical disc by the objectivelens 73 is performed, a threshold value TH ((b) to (g) of FIG. 13)corresponding to an all sum signal value AS-beamin obtained on the beamincident surface of the optical disc has been previously stored in thememory section 51 a of the control section 51 in order to detect whetherthe unknown optical disc has been loaded in the optical disc device 50(detection of presence of optical disc). The threshold value TH ispreset to be smaller than the all sum signal value AS-beamin obtained onthe beam incident surface of the optical disc.

An all sum signal value AS-cdref for CD signal surface reference ispreviously stored in the memory section 51 of the control section 51 toidentify a CD signal surface 12 of the CD 10 or a CD signal surface 25of the hybrid SACD 20 as a CD. The all sum signal value AS-cdref for theCD signal surface reference is smaller than the all sum signal valueAS-cd obtained on each of the CD signal surface 12 of the CD 10 and theCD signal surface 25 of the hybrid SACD 20, and usually larger than avalue of an all sum signal obtained on a signal surface of the otheroptical disc excluding the CD signal surface 12 of the CD 10 and the CDsignal surface 25 of the hybrid SACD 20.

Moreover, in order to identify the type of the unknown optical disc, inthe memory section 51 a of the control section 51, a threshold valueFETH (not shown) for detecting a reflectance of the signal surface ofthe optical disc by using a focus error signal FE and a threshold valueEVTH (FIGS. 14A and 14B) for detecting an envelope track state of a datareproducing signal RF are previously stored.

Furthermore, the lens bottom point voltage γ and the lens top pointvoltage δ at the time of starting obtained by calculation as describedabove, the focus search driving voltage Q corresponding to the all sumsignal value AS-dvd on the DVD signal surface 32 obtained by using thereference DVD-SL 30, and the focus search driving voltage Rcorresponding to the all sum signal value AS-cd on the CD signal surface12 obtained by using the reference CD 10 are previously stored in thememory section 51 a of the control section 51.

Here, in the present invention, the semiconductor laser 64 for DVD isstarted first in order to identify the type of the unknown optical discas described above. Thus, the operation of identifying the type of theunknown optical disc by using the semiconductor laser 64 for DVD will bedescribed first, and the operation of identifying the type of theunknown optical disc by using the semiconductor laser 63 for CD will bedescribed later as a modified example of the invention.

First, as shown in FIG. 10, in step S11, an optical disc whose type isunknown is loaded on the unillustrated turntable. Without rotating theunknown optical disc, the semiconductor laser 64 for DVD is started toirradiate an innermost peripheral side of the optical disc with a laserbeam from a beam incident surface side.

Next, in step S12, the laser beam from the semiconductor laser 64 forDVD is narrowed by the objective lens 73. The objective lens 73 islowered from a lens midpoint (I of FIG. 12) to a lens bottom point (IIof FIG. 12) corresponding to the lens bottom point voltage γ at the timeof starting as shown in FIG. 12 and FIG. 13 while the unknown opticaldisc of a rotation stopped state is irradiated with a laser beam whosewavelength is near 650 nm from the objective lens 73. Then, theobjective lens 73 is raised to a lens top point (V of FIG. 12)corresponding to the lens top point voltage δ at the time of starting.While raising the objective lens 73, an all sum signal AS from thephotodetector signal processing circuit 53 is inputted to the arithmeticoperation section 51 b of the control section 51 to be monitored. Notethat, an operation opposite to the above is possible. That is, theobjective lens 73 placed on standby at the lens midpoint is raised tothe lens top point, and then lowered from the lens top point toward thelens bottom point.

Next, in step S13, presence of an unknown optical disc is detected whileraising the objective lens 73. The detection of optical disc presence iscarried out by obtaining an all sum signal value AS-beamin (III of FIG.12) obtained on the beam incident surface of the unknown optical discwhile raising the objective lens 73, and making comparison at thearithmetic operation section 51 b of the control section 51 to determinewhether the all sum signal value AS-beamin is larger than the thresholdvalue TH ((b) to (g) of FIG. 13) previously stored in the memory section51 a of the control section 51. Here, when the disc is determined not tobe present (NO), the focus searching is canceled in step S14.

Incidentally, when the disc is determined not to be present (NO) in stepS13, instead of immediately proceeding to step S14, by raising theobjective lens 73 to the lens top point, and then by shifting theobjective lens 73 slightly to a position from the innermost peripheralside toward the outer peripheral side, detection of optical discpresence can be carried out more surely. Further, when the disc isdetermined not to be present (NO) in step S13, a return light from theoptical disc by the semiconductor laser 64 for DVD may have lowsensitivity to the recordable CD-R, CD-RW. In this case, thesemiconductor laser is switched to the semiconductor laser 63 for CD tocarry out detection of optical disc presence again. Accordingly, thedetection of optical disc presence can carried out more surely.

On the other hand, when presence of an optical disc is determined (YES)in step S13, a focus search driving voltage X corresponding to the allsum signal value AS-beamin obtained on the beam incident surface of theunknown optical disc is obtained by the focus search driving signalgeneration section 51 c of the control section 51 in step S15. Thisfocus search driving voltage X is stored in the memory section 51 a ofthe control section 51.

Next, in step S16, the objective lens 73 is raised to obtain an all sumsignal value AS-max (IV of FIG. 12) obtained on the signal surface ofthe unknown optical disc and a focus search driving voltage Ycorresponding to the all sum signal value AS-max by the focus searchdriving signal generation section 51 c of the control section 51. Thefocus search driving voltage Y is stored in the memory section 51 a ofthe control section 51.

Next, as shown in FIG. 11, in step S17, in order to identify a type ofthe unknown optical disc, an all sum signal value AS-max of a returnlight reflected on the signal surface of the unknown optical disc isdetermined by the following expression (1), and a distance from a lensmidpoint to the signal surface of the unknown optical disc is determinedwith the lens midpoint (natural position) of the objective lens 73 setas a reference by the following expression (2).As-max>AS-cdref  (1)

where

AS-max: all sum signal value on the signal surface of the unknownoptical disc

AS-cdref: all sum signal value for CD signal surface reference preset toidentify the CD 10 and the hybrid SACD 20 as a CD based on respective CDsignal surfaces 12, 25 thereofY>{(Q+2R)/3}  (2)

where

Y: focus search driving voltage corresponding to the all sum signalvalue AS-max on the signal surface of the unknown optical disc

Q: focus search driving voltage corresponding to the all sum signalvalue AS-dvd on the DVD signal surface of the reference DVD

R: focus search driving voltage corresponding to the all sum signalvalue AS-cd on the CD signal surface of the reference CD

In the expression (1), the all sum signal value AS-max is obtained instep S16, while the all sum signal value for the CD signal surfacereference AS-cdref is previously stored in the memory section 51 a ofthe control section 51 before shipping of the optical disc device 50 asdescribed above.

In this event, when the expression (1) is satisfied, the all sum signalvalue AS-max on the signal surface of the unknown optical disc is largerthan the preset all sum signal value for the CD signal surface referenceAS-cdref. However, it is impossible to determine that the signal surfaceof the unknown optical disc is the signal surface 12 of the CD 10 or thesignal surface 25 of the hybrid SACD only by the expression (1). Areason is that the expression (1) may be satisfied even by the othertype of an optical disc such as a high-reflection DVD to be describedlater. Hence, determination by the expression (2) becomes necessary.

That is, in the expression (2), the focus search driving voltage Y isobtained in step S16. On the other hand, the focus search drivingvoltage Q has been obtained beforehand from the reference DVD-SL 30before the shipping of the optical disc device 50, and the focus searchdriving voltage R has been obtained beforehand from the reference CD 10before the shipping of the same. Then, both focus search drivingvoltages Q and R has been previously stored in the memory section 51 aof the control section 51.

In the determination of the expression (2), the lens midpoint (naturalposition) of the objective lens 73 is set as the reference, and thedistance from the lens midpoint to the signal surface of the unknownoptical disc is converted into the focus search driving voltage. Then,when the expression (2) is satisfied, the objective lens 73 is focusedon the signal surface of the unknown optical disc, and the focus searchdriving voltage value Y corresponding to the signal surface is largerthan the focus search driving voltage {(Q+2R)/3} corresponding to thedistance from the lens midpoint of the objective lens 73 to the CDsignal surface 12 of the reference CD 10. Accordingly, the signalsurface of the unknown optical disc is regarded as the signal surface 12of the CD 10 or the signal surface 25 of the hybrid SACD.

Thus, when the expressions (1) and (2) are satisfied (YES), in step S18,the unknown optical disc is identified as a CD by the optical disc typeidentification section 51 d of the control section 51. In this case, theunknown optical disc is the CD 10 shown in (b) of FIG. 13 or the hybridSACD 20 shown in (d) of FIG. 13. Especially, since the hybrid SACD 20 isidentified simply as a CD to enable playing-back of only the CD signalsurface 25 thereof, no HD signal processing section for processing theHD signal surface 22 of the hybrid SACD 20 needs to be disposed in theRF signal demodulation circuit 56 (FIG. 3). Accordingly, the opticaldisc device 50 can be provided inexpensively. Subsequently, when thedisc is identified as a CD, the processing moves to step S22.

On the other hand, when neither of the expressions (1) and (2) aresatisfied (NO), in step S19, a distance from the beam incident surfaceof the unknown optical disc to the signal surface is determined by thefollowing expression (3) in order to identify a type of the unknownoptical disc.(Y−X)>{5×(R−Q)/3}  (3)

where

Y: focus search driving voltage corresponding to the all sum signalvalue AS-max on the signal surface of the unknown optical disc

X: focus search driving voltage corresponding to the all sum signalvalue AS-beamin on the beam incident surface of the unknown optical disc

R: focus search driving voltage corresponding to the all sum signalvalue AS-cd on the CD signal surface of the reference CD

Q: focus search driving voltage corresponding to the all sum signalvalue AS-dvd on the DVD signal surface of the reference DVD

In the expression (3), the focus search driving voltage Y is obtained instep S16, and the focus search driving voltage X is obtained in stepS15. Moreover, the focus search driving voltages R and Q are similar tothose of the expression (2).

In this case, when the expression (3) is satisfied (YES), while a resultof determination in step S17 shows that the all sum signal value AS-maxon the signal surface of the unknown optical disc is smaller than theall sum signal value for the CD signal surface reference AS-cdref, thefocus search driving voltage value (Y−X) corresponding to the distancefrom the beam incident surface of the unknown optical disc to the signalsurface is larger than the focus search driving voltage value{5×(R−Q)/3} corresponding to the distance from the beam incident surface11 a of the reference CD 10 to the CD signal surface 12. Thus, aposition of the signal surface of the unknown optical disc is consideredto be equal to that of the signal surface 12 of the CD 10. As a result,the unknown optical disc is identified as a CD by the optical disc typeidentification section 51 d of the control section in step S20. In thiscase, the unknown optical disc is the CD-R or CD-RW shown in (c) of FIG.13, and then the processing moves to step S22.

On the other hand, when the expression (3) is not satisfied (NO), instep S21, the unknown optical disc is identified as a DVD by the opticaldisc type identification section 51 d of the control section 51. In thiscase, the unknown optical disc is the DVD-SL 30 shown in (e) and (f) ofFIG. 13 or the DVD-DL 40 shown in (g) of FIG. 13.

Then, when the unknown optical disc is identified as a CD in step S18 orstep S20, the optical disc is subsequently rotated at a high speed bythe unillustrated spindle motor in step S22, and the semiconductor laser64 for DVD is switched to the semiconductor laser 63 for CD.

Meanwhile, when the unknown optical disc is identified as a DVD in stepS21, the optical disc is rotated at a high speed by the unillustratedspindle motor in step S23, and the operation of the semiconductor laser64 for DVD is continued. In this event, after the all sum signal valueAS-max (IV of FIG. 12) on the signal surface of the unknown optical discis obtained, the optical disc is rotated at a high speed while raisingthe objective lens 73 toward the lens top point (V of FIG. 12).

The aforementioned steps S15 to S23 are characterized in that theunknown optical disc is identified as a CD or a DVD by using the all sumsignal value AS-max obtained on the signal surface of the unknownoptical disc, the all sum signal value for the CD signal surfacereference AS-cdref preset to identify the CD 10 and the hybrid SACD 20as a CD based on respective CD signal surfaces 12, 25 thereof, the focussearch driving voltage X obtained by corresponding to the beam incidentsurface of the unknown optical disc, the focus search driving voltage Yobtained by corresponding to the signal surface of the unknown opticaldisc, the focus search driving voltage Q previously stored correspondingto the DVD signal surface 32 of the reference DVD-SL 30, and the focussearch driving voltage R previously stored corresponding to the CDsignal surface 12 of the reference CD 10. In order to further improveaccuracy of the type identification of the unknown optical disc, stepsS24 to S35 described below are used to identify a high reflection DVD ora low reflection DVD, a high reflection CD or a low reflection CD.

That is, when the unknown optical disc is identified as a DVD in stepS21, in step S24, a peak to peak (p-p) value of a focus error signal FEobtained in the photodetector signal processing circuit 53 is fetchedinto the arithmetic operation section 51 b of the control section 51.The p-p value of the focus error signal FE is compared with a thresholdvalue FETH (not shown) previously stored in the memory section 51 a ofthe control section 51 to determine a gain based on the focus errorsignal FE. In this event, the gain determination based on the focuserror signal FE is carried out between VI and VII of FIG. 12.

When the p-p value of the focus error signal FE is larger than thethreshold value FETH, a gain is maintained for the signal system of thephotodetector signal processing circuit 53 in step S25 to proceed tostep S27. Subsequently, pulling-in of the objective lens 73 is startedat timing of VIII of FIG. 12. On the other hand, when the p-p value ofthe focus error signal FE is smaller than the threshold value FETH, again-up command signal GUP (FIG. 3) is sent from the control section 51to the photodetector signal processing circuit 53 to increase the gain(gain-up) for the signal system in step S26, and the processing moves tostep S28. Subsequently, the pulling-in of the objective lens 73 isstarted at timing of VIII of FIG. 12.

Next, in steps S27 and S28, envelope determination is carried out for adata reproducing signal RF obtained in the photodetector signalprocessing circuit 53 mainly to identify a high reflection DVD or a lowreflection DVD, and to detect a CD mistakenly determined to be a DVD forone reason or another while the unknown optical disc is a CD.

Here, in the envelope determination of the data reproducing signal RF,when the CD signal surface 12 of the CD 10 or the CD signal surface 25of the hybrid SACD is played back as shown in FIG. 14A, a track pitch ofeach of the signal surfaces 12, 25 is wide, i.e., 1.6 μm. Accordingly, apeak and bottom waveform conspicuously appears for each crossing of atrack in the envelope of the RF signal, and a pulse waveform can begenerated for the peak and bottom waveform by using the threshold valueEVTH previously stored in the memory section 51 a of the control section51. As a result, the unknown optical disc can be identified as a CD.

On the other hand, when the DVD signal surface 32 of the DVD-SL 30 orthe first and second DVD signal surfaces 42, 45 of the DVD-DL 40 areplayed back as shown in FIG. 14B, a track pitch of each of the signalsurfaces 32, 42 and 45 is narrower and denser, i.e., 0.8 μm, comparedwith the CD. Accordingly, no peak and bottom waveform appears atcrossing of a track in the envelope of the RF signal. Thus, since nopulse waveform is generated even when the threshold value EVTH is used,the unknown optical disc can be identified as a DVD.

Therefore, if gain maintenance is determined for the signal system instep S25, and RF signal envelop determination is carried out in stepS27, the processing moves to step S22 when a disc is identified as a CD.When a disc is identified as a DVD, in step S29, the disc can beidentified as a read-only DVD-SL 30 or DVD-R (not shown) in which asignal layer is one layer and a reflectance is high as shown in (e) ofFIG. 13.

On the other hand, when gain-up is determined for the signal system instep S26, and RF signal envelope determination is carried out in stepS28, the processing moves to step S22 when a disc is identified as a CD.When the disc is identified as a DVD, in step S30, the disc can beidentified as a recordable DVD-SL 30 (DVD-RW) in which a signal layer isone layer and a reflectance is low as shown in (f) of FIG. 13, or aDVD-DL 40 in which a signal layer is constituted of two layers and areflectance is low as shown in (g) of FIG. 13.

Additionally, when the disc is identified as the CD 10 or the hybridSACD 20 among CDs in step S18, or when the disc is identified as CD-R orthe CD-RW among CDs in step S20, the optical disc is rotated at a highspeed in step S22; the semiconductor laser 64 for DVD is switched to thesemiconductor laser 63 for CD, and then gain determination is carriedout for the optical disc based on a focus error signal FE similarly tothe above-described case in step S31; gain maintenance is determined forthe signal system in step S32 when a p-p value of the focus error signalFE is larger than the threshold value FETH; and gain-up is determinedfor the signal system in step S33 when the p-p value of the focus errorsignal FE is smaller than the threshold value FETH. Thus, when the gainmaintenance is determined in step S32, the disc can be identified as ahigh reflection CD in step S34. The high reflection CD includes the CD10, the hybrid SACD 20, and the CD-R. On the other hand, when thegain-up is determined in step S33, the disc can be identified as a lowreflectance CD in step S35. The low reflectance CD includes the CD-RW.

Next, brief description will be given of an operation of identifying atype of an unknown optical disc by using the semiconductor laser 63 forCD, as modified example of the present invention with reference to FIGS.15 to 17.

FIG. 15 is a flowchart (1) of identifying a type of an unknown opticaldisc by staring the semiconductor laser for CD first. FIG. 16 is aflowchart (2) of identifying the type of the unknown optical disc bystarting the semiconductor laser for CD first. FIG. 17 is a flowchart(3) of identifying the type of the unknown optical disc by starting thesemiconductor laser for CD first.

In the case of identifying the type of the unknown optical disc bystarting the semiconductor laser 63 for CD first, a technical ideathereof is similar to that of identifying the type of the unknownoptical disc by staring the semiconductor laser 64 for DVD first.However, since especially a recordable optical disc that uses dyes haswavelength dependence in response to a laser beam, if the semiconductorlaser 63 for CD is activated, a result of identification is differentfrom that of the semiconductor laser 64 for DVD. Description of themodified example will focus on differences from the case of starting thesemiconductor laser 64 for DVD first.

To begin with, as shown in FIG. 15, only step S41 among operations ofsteps S41 to S46 is different from the steps S11 to S16 shown in FIG.10, in which the semiconductor laser 64 for DVD is started first, inthat the semiconductor laser 63 for CD emitting a laser beam having awavelength of near 780 nm is started first. In the middle of raising theobjective lens 73 from the lens bottom point toward the lens top pointin step S42, detection of optical disc presence (step S43), acquisitionof a focus search driving voltage X corresponding to an all sum signalvalue AS-beamin obtained on the beam incident surface of the unknownoptical disc (step S45), and acquisition of an all sum signal valueAS-max obtained on the signal surface of the unknown optical disc and afocus search driving voltage Y corresponding to the all sum signal valueAS-max (step S46) are sequentially carried out.

Subsequently, as shown in FIG. 16, in step S47, in accordance with thewavelength dependence of the semiconductor laser 63 for CD on theoptical disc, an all sum signal value AS-cdref for CD signal surfacereference itself for identifying the CD 10, the hybrid SACD, and CD-R asa CD based on the CD signal surface 12 of the CD 10, the CD signalsurface 25 of the hybrid SACD 20 or the CD signal surface (not shown) ofthe CD-R is preset by making a slight change from the case of thesemiconductor laser 64 for DVD. Thus, when all sum signalvalue-AS-max-determination of a return light reflected on the signalsurface of the unknown optical disc is carried out by the expression(1), and distance determination from the lens midpoint to the signalsurface of the unknown optical disc with the lens midpoint (naturalposition) of the objective lens 73 set as a reference is carried out bythe expression (2), if the expressions (1) and (2) are both satisfied(YES), the unknown optical disc is identified as a CD by the opticaldisc type identification section 51 d of the control section 51 in stepS48. In this case, however, a difference from the case of starting thesemiconductor laser 64 for DVD first is that the unknown optical disc isthe CD 10 shown in (b) of FIG. 13 or the hybrid SACD 20 shown in (d) ofFIG. 13, and a CD-R is included.

Next, assuming that neither of the expressions (1) and (2) are satisfied(NO), if the expression (3) is satisfied (YES) when distancedetermination from the beam incident surface of the unknown optical discto the signal surface is carried out by the expression (3) in step S49,the unknown optical disc is identified as a CD by the optical disc typeidentification section 51 d of the control section 51 in step S50. Inthis case, however, a difference from the case of starting thesemiconductor laser 64 for DVD first is that the unknown optical disc isonly a CD-RW.

On the other hand, if the expression (3) is not satisfied (NO), theunknown optical disc is identified as a DVD by the optical disc typeidentification section 51 d of the control section 51 in step S51. Inthis case, the unknown optical disc is the DVD-SL 30 shown in (e) and(f) of FIG. 13, or the DVD-DL 40 shown in (g) of FIG. 13, which issimilar to the case of starting the semiconductor laser 64 for DVDfirst.

Subsequently, the optical disc identified to be the DVD in step S51 isrotated at a high speed in step S54, and the semiconductor laser 63 forCD is switched to the semiconductor laser 64 for DVD to carry out gaindetermination for the optical disc identified to be the DVD based on afocus error signal FE (step S55) as shown in FIG. 17. After theoperation is divided into gain maintenance for the signal system (stepS56) and gain-up for the signal system (step S57), envelopedetermination is carried out for data reproducing signals RF (steps S58,S59). Accordingly, as in the case of staring the semiconductor laser 64for DVD first, a high reflection DVD (DVD-SL/DVD-R) is identified instep S60, while a low reflection DVD (DVD-DL/DVD-RW) is identified instep S61 as shown in FIG. 17.

Further, a CD mistakenly determined to be a DVD for one reason oranother while the unknown optical disc is a CD is detected in theenvelope determination of the data reproducing signals RF (steps S58,S59). Here, if it is detected to be a CD, the semiconductor laser 64 forDVD is switched to the semiconductor laser 63 for CD in step S62. Gaindetermination is carried out again based on the focus error signal FE instep S63. The processing moves to step S64 (described later) if a resultof the gain determination shows gain maintenance for the signal system.On the other hand, the processing moves to step S66 (described later) ifgain-up is determined for the signal system.

Additionally, if the CD 10, the hybrid SACD 20 or the CD-R is identifiedamong CDs in step S48, the optical disc is rotated at a high speed instep S52. If the CD-RW is identified among CDs in step S50, the opticaldisc is rotated at a high speed in step S53.

Subsequently, gain maintenance for the signal system is carried out forthe optical disc identified to be the CD 10, the hybrid SACD 20 or theCD-R among CDs in step S64. If a high reflection CD is identified instep S65, this high reflection CD includes the CD 10, the hybrid SACD 20and the CD-R.

On the other hand, gain-up for the signal system is carried out for theoptical disc identified to be the CD-RW in step S66. If a low reflectionCD is identified in step S67, this low reflection CD includes only theCD-RW.

As apparent from the foregoing, irrespective of the semiconductor laser64 for DVD or the semiconductor laser 63 for CD, after the highreflection DVD or the low reflection DVD, the high reflection CD or thelow reflection CD are identified, it is possible to quickly carry outswitching of the semiconductor laser and processing of the signal systemat a high speed in accordance with the result of identification.

According to the focus searching method of the optical disc and theoptical disc device of the present invention which have been describedin detail, a focus search driving voltage corresponding to a signalsurface of an optical disc is obtained on the basis of detectioninformation from a photodetector when an objective lens is focused onthe signal surface of the optical disc in the middle of raising orlowering the objective lens placed on standby at a lens midpoint betweena temporarily set lens bottom point and a temporarily set lens top pointaccording to a temporarily set lens bottom point voltage and atemporarily set lens top point voltage. Then, a lens bottom pointvoltage and a lens top point voltage at the time of device starting areobtained by an arithmetic operation program based on the focus searchdriving voltage and predetermined factors, and then a lens bottom pointcorresponding to the lens bottom point voltage is set to be nearer tothe lens midpoint side than the temporarily set lens bottom point whilea lens top point corresponding to the lens top point voltage is set tobe nearer to the lens midpoint side than the temporarily set lens toppoint. For this reason, the moving distance of the objective lens at thetime of the focus search can be set short and in other words the movingtime of the objective lens can be reduced, to thereby quickly shift to adata reproduction operation after the focus search.

It should be understood that many modifications and adaptations of theinvention will become apparent to those skilled in the art and it isintended to encompass such obvious modifications and changes in thescope of the claims appended hereto.

1. A focus searching method in which a laser beam is irradiated on anoptical disc from a beam incident surface side thereof through anobjective lens, and a return light from a signal surface of the opticaldisc is received by a photodetector in the middle of raising or loweringthe objective lens placed on standby at a lens midpoint between a lowerlens bottom point and an upper lens top point based on a focus searchdriving signal during focus searching, and whether the objective lens isfocused on the signal surface of the optical disc while keeping apredetermined working distance to the beam incident surface of theoptical disc is determined on the basis of the detection informationfrom the photodetector, the method comprising the steps of: storing inadvance a temporarily set lens bottom point voltage corresponding to atemporarily set lens bottom point temporarily set at a lower positionthat has more room than a predetermined working distance of theobjective lens, and a temporarily set lens top point voltagecorresponding to a temporarily set lens top point temporarily set at aposition slightly before the objective lens abuts on the beam incidentsurface of the optical disc; obtaining a focus search driving voltagecorresponding to the signal surface of the optical disc based on thedetection information from the photodetector when the objective lens isfocused on the signal surface of the optical disc in the middle ofraising or lowering the objective lens placed on standby at the lensmidpoint between the temporarily set lens bottom point and thetemporarily set lens top point based on the temporarily set lens bottompoint voltage and a temporarily set lens top point voltage; andobtaining a lens bottom point voltage and a lens top point voltage atthe time of device starting by an arithmetic operation program based onthe focus search driving voltage and a predetermined factor, and settingthe lens bottom point corresponding to the lens bottom point voltage tobe nearer to the lens midpoint side than the temporarily set lens bottompoint while setting the lens top point corresponding to the lens toppoint voltage to be nearer to the lens midpoint side than thetemporarily set lens top point.
 2. An optical disc device in which alaser beam is irradiated on an optical disc from a beam incident surfaceside thereof through an objective lens, and a return light from a signalsurface of the optical disc is received by a photodetector in the middleof raising or lowering the objective lens placed on standby at a lensmidpoint between a lower lens bottom point and an upper lens top pointbased on a focus search driving signal during focus searching, andwhether the objective lens is focused on the signal surface of theoptical disc while keeping a predetermined working distance to the beamincident surface of the optical disc is determined on the basis of thedetection information from the photodetector, the device comprising:storing means for storing in advance a temporarily set lens bottom pointvoltage corresponding to a temporarily set lens bottom point temporarilyset at a lower position that has more room than a predetermined workingdistance of the objective lens, and a temporarily set lens top pointvoltage corresponding to a temporarily set lens top point temporarilyset at a position slightly before the objective lens abuts on the beamincident surface of the optical disc; focus search driving signalgenerating means for obtaining a focus search driving voltagecorresponding to the signal surface of the optical disc based on thedetection information from the photodetector when the objective lens isfocused on the signal surface of the optical disc in the middle ofraising or lowering the objective lens placed on standby at the lensmidpoint between the temporarily set lens bottom point and thetemporarily set lens top point based on the temporarily set lens bottompoint voltage and a temporarily set lens top point voltage; andarithmetic operating means for obtaining a lens bottom point voltage anda lens top point voltage at the time of device starting by an arithmeticoperation program based on the focus search driving voltage and apredetermined factor, and setting the lens bottom point corresponding tothe lens bottom point voltage to be nearer to the lens midpoint sidethan the temporarily set lens bottom point while setting the lens toppoint corresponding to the lens top point voltage to be nearer to thelens midpoint side than the temporarily set lens top point.